The broad objective of this project is to understand the biology of serum hormone transport proteins and the role that they play in human disease. Recent research findings include: (1) The elucidation of the relative roles of plasma testosterone bound to albumin and that bound to sex-hormone binding globulin in determining testosterone bioavailability to the tissues, and (2) the application of sex-hormone binding globulin as a biochemical index of thyroid hormone action to demonstrate the maintenance of a euthyroid state during physical condition in humans. Future investigations under this project will delineate the role of human adrenal function in modulating the plasma level of corticosteroid-binding globulin and explore pharmacological and pathological factors that modulate serum hormone transport proteins. Effort will also be placed on development of an in vitro system for elucidation of the mechanisms of modulation of intracellular hormone levels by plasma constituents.